In today’s society, stainless steel has become one of the important metal materials, widely used in construction, food processing, medical equipment, the chemical industry, shipbuilding, and other fields. As a material with excellent properties, stainless steel has become one of the preferred materials in various industries due to its high corrosion resistance, high strength, high-temperature tolerance, easy cleaning, and low maintenance.
This article will introduce and analyze the 4 types of stainless steel, namely austenitic, ferritic, duplex, and martensitic. Through an in-depth understanding of these four types, you can better understand the properties, advantages, and disadvantages of stainless steel, and then apply it to more practical scenarios and fields.
Definition and Classification Types of Stainless Steel
What is Stainless Steel?
Stainless steel refers to an iron alloy containing at least 10.5% chromium, the main characteristics of which are good corrosion resistance and good mechanical properties. In addition to chromium, stainless steel may also contain other alloying elements, such as nickel, molybdenum, titanium, copper, etc., as well as a small amount of carbon, silicon, manganese, and other elements.
Classification of Stainless Steel
According to the alloying elements and crystal structure in stainless steel, it can be divided into many types. The following is the classification methods of stainless steel:
1. Classification by composition: According to the composition of alloy elements in stainless steel, it can be divided into chromium stainless steel, chromium-nickel stainless steel, chromium-nickel-molybdenum stainless steel, duplex stainless steel, etc.
2. Classification by crystal structure: According to the crystal structure of stainless steel, it can be divided into austenitic stainless steel, ferritic stainless steel, martensitic stainless steel, duplex stainless steel, etc.
3. Classification by use: According to the application fields and uses of stainless steel, it can be divided into tableware stainless steel, medical stainless steel, chemical stainless steel, construction stainless steel, mechanical stainless steel, etc.
Through different classification methods, we can better understand the properties and characteristics of stainless steel, choose appropriate stainless steel materials, and apply them in different fields and scenarios.
Austenitic Stainless Steel
A. Features and Uses
Austenitic stainless steel has the following characteristics:
- Good corrosion resistance, able to resist the corrosion of most chemical substances.
- Good strength and plasticity, easy to process into parts and components of various shapes and sizes.
- Good heat processing performance, able to withstand processing and use under high temperatures.
- It can be used in a low-temperature environment and is not easily affected by low-temperature embrittlement.
It is suitable for the manufacture of parts with high requirements, such as pneumatic components, aerospace components, medical equipment, food processing equipment, etc.
B. Alloy Composition and Structure
The main alloying elements of austenitic stainless steel are chromium and nickel, of which the content of chromium is usually between 16% and 26%, and the content of nickel is usually between 6% and 22%. In addition, austenitic stainless steel may also contain other alloying elements, such as molybdenum, titanium, copper, etc. The addition and control of these alloying elements can affect the performance and corrosion resistance of stainless steel.
The structure of austenitic stainless steel is an austenite crystal structure, and the crystal structure has high density, good mechanical properties and corrosion resistance. In different manufacturing processes, the stability and composition of the austenite crystal structure can be adjusted by controlling the content and addition methods of alloying elements such as chromium, nickel, and molybdenum, so as to adapt to different uses and environments.
C. Typical Application
Austenitic stainless steel is widely used in the following fields and occasions:
- Equipment and pipelines in chemical, petroleum, natural gas, and other fields.
- Medical equipment, surgical instruments, syringes, and other medical equipment.
- Food processing equipment, tableware, kitchen utensils, etc.
- High-precision fields such as aerospace and automobile manufacturing.
- Building decoration materials, bathroom equipment, household items, etc.
- Equipment and components in marine, environmental protection, new energy, and other fields.
Ferritic Stainless Steel
A. Features and Uses
The main characteristic of ferritic stainless steel is that it contains a high proportion of ferrite, usually greater than 50%. Ferritic stainless steel has relatively poor corrosion resistance, but it has high strength and hardness and is magnetic. Ferritic stainless steel is suitable for the manufacture of parts and components that require high strength, high hardness, and wear resistance, such as tools, bearings, valves, etc.
B. Alloy Composition and Structure
The main alloying elements of ferritic stainless steel are chromium and molybdenum, in which the content of chromium is usually between 12% and 30%, and the content of molybdenum is usually less than 5%. The microstructure of ferritic stainless steel is a ferrite crystal structure, and the crystal structure is relatively large and scattered, which is prone to intergranular corrosion and stress corrosion.
C. Typical Application
Ferritic stainless steel is mainly used in the following fields and occasions:
- Mechanical parts and components such as knives, bearings, valves, pumps, etc.
- Auto parts, automobile exhaust systems, etc.
- Components in food processing equipment that require wear resistance.
- Mining equipment and drilling equipment.
- Cement production equipment and metallurgical equipment and other fields that require high strength and wear resistance.
Duplex Stainless Steel
A. Features and Uses
Duplex stainless steel is stainless steel that contains both austenitic and ferritic crystal structures, so it has the advantages of both austenitic and ferritic stainless steel. Duplex stainless steel has high strength, good corrosion resistance, and good welding performance, and is suitable for use in high temperature, high pressure, and corrosive environments.
B. Alloy Composition and Structure
The alloy composition of duplex stainless steel mainly includes chromium, nickel, molybdenum and other elements, in which the content of chromium is usually between 18% and 25%, the content of nickel is usually between 4% and 8%, and the content of molybdenum is usually 0%. to 5%. The microstructure of duplex stainless steel is a mixed crystal structure of austenite and ferrite, the crystal structure is relatively small and uniform and has good comprehensive properties.
C. Typical Application
Duplex stainless steel is mainly used in the following fields and occasions:
- Pipelines, storage tanks, containers, and other equipment in petrochemical, chemical, and marine development fields.
- Parts in food processing equipment that require high corrosion resistance and good weldability.
- Auto parts, train bodies, bridges, and other fields require high strength and corrosion resistance.
- Stainless steel materials in the field of construction and decoration, such as stainless steel tableware, kitchen equipment, etc.
- Highly demanding fields such as medical devices, electronic equipment, and instrumentation.
Martensitic Stainless Steel
A. Features and Uses
Martensitic stainless steel is a stainless steel with high strength, good corrosion resistance, and good processability. Martensitic stainless steel contains a large amount of martensite in its structure by controlling the cooling rate and alloy composition during the manufacturing process, so as to obtain high strength and good corrosion resistance. Martensitic stainless steel is suitable for occasions that require high strength and good corrosion resistance, such as machinery manufacturing, aerospace, chemical, and other fields.
B. Alloy Composition and Structure
The alloy composition of martensitic stainless steel usually includes elements such as chromium, nickel, molybdenum, and titanium. Among them, the content of chromium is usually between 10% and 30%, the content of nickel is between 0% and 10%, the content of molybdenum is between 0% and 5%, and the content of titanium is usually between 0% and 2%. between. The structure of martensitic stainless steel contains a large amount of martensite, and the content of martensite can be adjusted by controlling the cooling rate. In general, the faster the cooling rate, the higher the martensite content.
C. Typical Application
Martensitic stainless steel is mainly used in the following fields and occasions:
- Parts that require high strength and good corrosion resistance in the field of mechanical manufacturing, such as gears, bearings, etc.
- Structural parts that require high strength and good corrosion resistance in the aerospace field, such as aero engines, aircraft parts, etc.
- Equipment and pipelines that require high strength and good corrosion resistance in the chemical and petrochemical fields.
- Highly demanding fields such as medical devices and electronic devices.
In Conclusion:
Stainless steel is a material widely used in industry and life. According to its structure and performance characteristics, it can be divided into four types: austenitic, ferritic, duplex, and martensitic stainless steel. Each stainless steel has its own unique characteristics, alloy composition, and typical application areas.
Austenitic stainless steel has good corrosion resistance and processing performance, and is widely used in chemical, pharmaceutical, food, and other fields; ferritic stainless steel has good heat resistance and wear resistance and is suitable for high temperature, high pressure, and severe wear. Duplex stainless steel has high strength and good plasticity, and is suitable for some occasions that require high strength and good toughness at the same time; martensitic stainless steel has high strength and good corrosion resistance and is suitable for machinery manufacturing, aerospace, chemical industry, and other fields.
The classification and application of stainless steel have been extensively researched and applied. In future development, as people have higher and higher requirements for the application of stainless steel, the research and application of stainless steel will continue to advance and make greater contributions to the development and progress of society.